I don't collect as much games in general, but PC has always been my biggest "collection", even if I don't count the dozens of digital games I own. I still have a number of my old PC games in a CD case and I've casually been collecting PC games for their boxes, because I think PC game are way better than most console game boxes, due to the lack of uniformity. I know some might disagree with that, but I look at it like a library and how most books aren't going to be the same, so it makes them all stand out more compared to everything having a matching shape and color scheme with small text on the box being the only standout element.
Least might be Switch. Not just because it's newer, but I generally find that there aren't as many games that interest me on it. Outside of the rare exclusive, I only play on my Switch when I purposefully choose to play a platformer game on it, because usually it's not gonna run any worse and those types of games are great portable, the few times I need it that is. Bloodstained was an outlier with this decision lol